In a G-reg you need to do 3 takeoffs and 3 landings, all during official UK-CAA night (official sunset + 30 mins).
They need to be done either with an instructor in the RHS (who himself needs to be night passenger current, or hold a valid JAA IR which exempts one from the 90 day requirement) or with nobody else in the aircraft.
In an N-reg the rules are slightly different, and the 3+3 need to be done after sunset + 1 hour. Night flight is logged after sunset + 30 mins (the 30 mins is actually an approximation but is widely used) but the night passenger carriage renewal needs ss+1hr.
I hope I got all that right
Nearly.
In a G Reg to carry passengers you must have done 3 take offs and landings in 90 days as sole manipulator of the controls.
If you wish to exercise the privileges of the licence at night then
one of these must have been at night.
You can do these solo or if required as a dual flight with an Instructor.
A JAA IR does not exempt you from the 90 day passenger carrying rule, only from the night currency element.